This invention relates to organic electroluminescent devices, especially organic electroluminescent devices containing aminostyrylnaphthalene compounds useful as electron transport materials, hole transport materials or light emitting materials, the aminostyrylnaphthalene compounds useful in the organic electroluminescent devices and their synthesis intermediates, and production processes of these compounds and intermediates.
In recent years, organic electroluminescent devices (EL devices) are attracting attention as a candidate for flat panel displays which can produce natural light, have a high response speed and have no visibility angle dependency, and accordingly, there is an increasing interest on organic materials as their constituents. Among such organic materials, however, there are not many materials capable of forming stable red-light emitting layers in particular. Finding of such materials has, therefore, become an indispensable requirement for the realization of full-color, organic electroluminescent devices.
As light-sensitive materials for electrophotography, aminostyryl compounds are disclosed, for example, in Japanese Patent Laid-open No.: Hei 5-105645, 2001-051433, 2002-131943, 2002-116560, 2002-099103, 2002-072511, 2002-040677, 2002-040676, 2002-031901, 2001-337469, 2001-337649, and 2000-214610. However, these compounds contain no electron attracting group in their molecules and hence, cannot be used for such applications as red-color emitting materials for organic electroluminescent devices.
As materials for organic electroluminescent devices, certain compounds are disclosed in Japanese Patent Laid-open No. Hei 3-200889, Hei 5-194943, and 2002-226722. As illustrative materials employed in white-light organic electroluminescent devices, other materials are disclosed in Japanese Patent Laid-open No. Hei 6-207170. These materials are, however, not for the emission of red light either. Further, materials with one or more styryl groups contained in combination with one or more triphenylamino groups are proposed in Japanese Patent Laid-open No.: Hei 5-320632, Hei 6-100857, Hei 9-268284, Hei 11-040359, Hei 11-102784, and Hei 10-245549. These materials, however, cannot be used for the emission of red light either.
Aminostyryl compounds useful as red-light emitting materials in organic electroluminescent devices are led by the aminostyryl compounds disclosed in Inorganic and Organic Electroluminescence '96 Berlin, p. 101, 1996; Journal of the Korean Chemical Society (1999), 43(3), 315-320; Bulletin of the Korean Chemical Society (2001), 22(2), 228-230; and Journal of the Korean Chemical Society (1999), 43(3), 315-320, and include those disclosed in Japanese Patent Laid-open No.: 2000-230132, 2002-022672, 2001-2883772, 2001-106657, and 2001-106658. Further, their application examples are reported in Japanese Patent Laid-open No.: Hei 11-329730, Hei 11-329731, 2000-012225, 2000-012228, 2000-012227, 2000-012226, 2001-305754, and 2000-136168. As described in Japanese Patent Laid-open No. 2002-134276, 2001-291591, 2001-307884 and 2001-307885, two or more of these materials may be positively combined together for use.
As the molecular structures of the materials referred to in the above, many of them have structures symmetrical relative to the molecular long axes thereof. To obtain an emission maximum at an optimal wavelength or to permit the exhibition of improved evaporation upon fabrication of organic electroluminescent devices many of which are fabricated by vacuum evaporation, however, asymmetrical structures may be effective in certain instances as disclosed in Japanese Patent Laid-open NO.: 2002-226722, 2001-288377, 2001-110570 (especially, page 4, right column, line 40 to page 5, right column, line 4 from the bottom; page 7, right column, line 30 to page 8, left column, line 17; FIG. 1 to FIG. 8), 2001-110571 and 2000-173773.
Japanese Patent Laid-open No. 2002-208488, on the other hand, discloses that such asymmetrical structures are also effective as structural units for polymers. Further, their applications as multiphoton absorbers are also considered to be promising as disclosed in Science (1998), 281(11), 1653; WO 2001-096409; NATO Science Series, 3: High Technology (2000), 79 (Multiphoton and Light Driven Multielectron Processes in Organics), 53-65; Journal of Chemical Physics (2000), 113(10), 3951-3959; Journal of Physical Chemistry A (2001), 105(51), 11488-11495; Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) (1998), 39(2), 1116; and Materials Research Society Symposium Proceedings (1998), 488 (Electrical, Optical, and Magnetic Properties of Organic Solid-State Materials IV), 217-226.
It is difficult to develop stable, high-luminance red-light emitting devices. Examples of those reported to date include a red-light emitting device making use of tris(8-hydroxyquinoline)aluminum (hereinafter abbreviated as “Alq3”) doped with 4-dicyanomethylene-6-(p-dimethylaminostyryl)-2-methyl-4H-pyran (hereinafter abbreviated as “DCM”) (Chem. Funct. Dyes, Proc. Int. Symp., 2nd, p. 536, 1993). As an example having achieved a reduction in the high crystallinity of DCM, there is 4-dicyanomethylene-6-(p-dimethylaminostyryl)-2-(t-butyl)-4H-pyran (hereinafter abbreviated as “DCJTB”) disclosed in Macromol. Synmpt., 125, 49, 1997. However, their reliability such as service life is not satisfactory as display materials.
In the development of organic electroluminescent devices, selection of light emitting materials is the most important theme in assuring reliability for the devices. The aminostyrylnaphthalene compounds disclosed in Japanese Patent Laid-open NO. 2001-110570 are excellent in color purity and high in fluorescence quantum yield and moreover, can form stable, amorphous thin films. Nonetheless, it is the current situation that there is still an outstanding desire for the realization of a red-light emitting device of high luminance, high stability and high color purity.